Process for preparing finely particled nickel powder

ABSTRACT

A process is disclosed for preparing finely particled metallic nickel powder, with spheroidal form, having dimensions lower than 1 micron. Bis-acrylonitrile-nickel is suspended in methanol, and the suspension is heated at temperatures between 100* and 200*C, and preferably at 150*-180*C, up to the complete decomposition. During the heating of the suspension, hydrogen is introduced under pressure.

United States Patent 1191 Montino et al.

1 51 Jan. 16, 1973 [54] PROCESS FOR PREPARING FINELY PARTICLED NICKEL POWDER [7'5] Irivehtorffihricb "Montino, C'lEMohfrrato; Franco Guerrieri, Novara,

both of Italy [22] Filed: May 14, 1970 211 App]. No.: 37,294

[30] Foreign Application Priority Data 3,573,292 3/1971 Wilke et al. ..260/242 OTHER PUBLICATIONS G. N. Schrauzer, J. Am. Chem. Soc., 81(1959), 5310-5312 Primary Examiner0scar R. Vertiz Assistant ExaminerHoke S. Miller Attorney-Stevens, Davis, Miller & Mosher [5 7] ABSTRACT A process is disclosed for preparing finely particled metallic nickel powder, with spheroidal form, having dimensions lower than 1 micron. Bis-acrylonitrilenickel is suspended in methanol, and the suspension is heated at temperatures between 100 and 200C, and preferably at l50l80C, up to the complete decomposition. During the heating of the suspension, hydrogen is introduced under pressure.

2 Claims, No Drawings PROCESS FOR PREPARING FINELY PARTICLED NICKEL POWDER The present invention relates to a process for preparing powder of metallic nickel. More particularly, it relates to a process for preparing finely divided metallic nickel powder below 1 micron in particle size, and having a spheroidal form.

Metallic powders having a spherical form with a diameter lower than 1 micron, and with a homogeneous distribution of the diameters, are used more and more in powder metallurgy because of the greater uniformity and the better properties of the end product. They are used, for example, either for making sintered alloys based on Ni-Cr-Co or based on Ni-Cr- A1 resistant to high temperatures, or for making magnetic sintered alloys based on Fe-Ni, or for making porous barriers based on nickel employed in the separation in the gaseous phase of uranium isotopes.

It is already known to produce powdered metallic nickel by thermal decomposition of nickel tetracarbonyl, of nickel oxalate and of formate. It is also known to produce powdered pure metallic nickel by the reduction of nickel oxide, nickel hydrate and nickel carbonate. The process more frequently used on an industrial scale consists in carrying out the steam pyrolysis of nickel tetracarbonyl, diluted in an inert gas, at a temperature ranging from 200 to 250C. In some cases, the decomposition is carried out in fuel oils or in biphenyl mixed with biphenyl-oxide.

Those processes involve the drawback of producing powdered nickel in which the particles have a diameter ranging from 2 to 5 microns. Such a particle size renders the metallic nickel thus obtained not very suitable, or in some instances even unsuitable, for the above mentioned uses.

Object of the present invention is therefore to provide a simple and economical process for preparing finely divided nickel powders which shall be free of the drawbacks of the prior art.

According to the present invention, finely divided metallic nickel powder, with spheroidal form and having dimensions lower than 1 micron, is obtained by suspending bis-acrylonitrile-nickel in methanol, and thereupon heating the resulting suspension at temperatures ranging from 100 to 200C, preferably from 150 to 180C, up to the complete decomposition.

The pyrolysis is carried out in a reactor having vitrified walls; the bis-acrylonitrile-nickel is suspended in methanol, inert towards the complex and wherein the complex is insoluble and brought to the determined temperature with stirring.

The concentration of the complex ranges from 1 to 20 percent, and preferably from 5 to 10 percent. The decomposition of the complex starts at about 110C and is carried out in a short time, at temperatures higher than 120C; the decomposition is practically ended when the suspension has become black and no longer shows red particles of bis-acrylonitrile-nickel.

The metallic nickel thus obtained is pyrophoric and may retain up to 15 percent of organic impurities. The purification is carried out by introducing hydrogen 10-100 atm) into the autoclave or other reaction vessel at the reaction temperature, and hydrogenating the organic impurities the percentage of which is thereby lowered to 3-4 percent.

EXAMPLE 15 g of bis-acrylonitrile-nickel* (*Bis-acrylonitrilenickel, (Cl-l =CH-CN) Ni, was prepared from nickelcarbonyl and acrylonitrile according to the method described by G.N. Schrauzer in J.Am.Chem. Soc., 81(1959), 5310-12.) were suspended in 400 cc of methanol and transferred, in N stream, into a 3.3 liter autoclave having enameled walls, and provided with a blade stirrer and heated by an oil jacket.

The temperature was raised to 160C over a period of two hours, whereupon hydrogen at 40 atm. was charged into the auto-clave and the stirring was continued at 160C for 2 hours. The autoclave was cooled to ambient temperature by maintaining always the mixture under stirring, then methanol and propylamine (formed by hydrogenation of acrylonitrile) were decanted.

The nickel thus obtained was washed 3 times with methanol and dried under vacuum. The nickel powder obtained in this manner was pyrophoric; it contained 3 percent ofC. 0.5 percent of H and 0.6 percent of N.

Granulometric analysis showed that 94 percent of the granules had a diameter ranging from 32 to 97 nanometers (milli-mi crons) and that 64.7 percent of the particles came within the limited zone of 57 nanometers i 20 percent (from 46 to 68 nanometers). The shape of the granules was spheroidal.

What is claimed is:

l. A process for preparing finely divided metallic nickel powder, with spheroidal form, having dimensions lower than 1 micron, wherein bis-acrylonitrilenickel is suspended in methanol, and the suspension is heated under hydrogen pressure at temperatures between 100 and 200C, up to the complete decomposition.

2. A process as defined in claim 1, wherein the temperatures are in the range 180C. 

2. A process as defined in claim 1, wherein the temperatures are in the range 150* - 180*C. 